This invention relates to thermometers and it is particularly concerned with improvements in hot spot thermometers.
While a hot spot thermometer may have other applications, it is especially suited for use in sensing temperature changes in a fluid cooled electric transformer.
A hot spot thermometer is so named because of its structural characteristics whereby it is enabled to be located for temperature monitoring purposes at the spot of hottest temperature development in a transformer. This spot is between the coils of the transformer winding.
This type of thermometer has various advantages. Because it is applied to the hottest area of the transformer, it obtains not only a more accurate reading but also a more rapid indication of temperature changes than would be otherwise provided.
A hot spot thermometer is known from U.S. Pat. No. 3,960,017. It utilizes a high heat resistant ceramic body insertable between the coils of a transformer winding and containing a heat sensitive dielectric rod adapted to vary passage of light through fibre optic elements to produce in an external read-out instrument electrical signals indicative of temperature changes developing in the transformer.
An object of the present invention is to provide a hot spot thermometer which utilizes a high heat resistant ceramic body insertable between the coils of a transformer winding and containing a heat sensitive rod which is cooperable with a closed tube containing a circulating gas to produce, according to variations in temperature in the transformer winding, pressure changes in the circulating gas, the pressure changes being readable on an associated pressure gage.
In accordance with the invention, there is provided the combination comprising an electrical transformer apparatus having a tank containing cooling fluid in which the coils of a transformer winding are immersed, a thermometer unit having a hollow open-ended body of ceramic dielectric material inserted into a space between the coils, the body being connected in a closed circuit filled with gas, a pump connected in the circuit for circulating the gas about the circuit, a heat sensing element of dielectric material arranged in the hollow of the body having response to temperature changes developing in the transformer winding to cause corresponding variations in the pressure of the circulating gas, and a sight gas pressure gage connected in the circuit adapted to indicate said pressure variations.